Molecular Diagnosis of the Philadelphia Chromosome in Acute Lymphoblastic Leukemia

The Philadelphia (Ph(1)) chromosome was the first specific chromosomal abnormality to be consistently associated with a particular neoplasm, in this case chronic myelogenous leukemia (CML,)(1). Formed by a reciprocal translocation between chromosomes 9 and 22(2), the 22q-, or Ph(1) chromosome is found in the malignant cells of more than 90% of patients with CML(3). The presence of the molecular equivalent of a Ph(1) chromosome is such a consistent finding in CML that it IS now the basis of a diagnostic test in routine clinical use.